Cholesterol and cholesterol esters are lipophilic substances which occur in numerous important foods of animal origin, for example egg yolk, meat, animal fats and the like.
Increased cholesterol levels in the blood serum of humans are regarded as being a risk for arteriosclerosis and of coronary heart disease.
By means of a reduction of the intake of cholesterol by foods, in pathological cases the endeavor is made to achieve the normal cholesterol values in the blood serum again. For that reason, there is a great interest in clearly reducing the content of cholesterol and of cholesterol esters in fat-rich foods of animal origin.
A significant problem is thereby retaining the sensory and nutritional-physiological properties of the foods as much as possible.
Although a number a processes are known for the isolation of cholesterol and of cholesterol esters, these methods are not suitable for the reduction of the cholesterol content of foods since they cause chemical changes in important components of the starting material, for example proteins, triglycerides and the like.
A relatively gentle process which has recently become known uses carbon dioxide high pressure extraction for the removal of cholesterol and of cholesterol esters (cf. V. Krukonis, Supercritical Fluid Processing, International Symposium on Supercritical Fluids, Nice, 1988).
This process is admittedly characterized by the physiological safety of the carbon dioxide used as extraction agent but working at a high pressure is technically rather expensive. Furthermore, with the use of this process unter gentle conditions, cholesterol and cholesterol esters cannot be removed selectively because triglycerides are also extracted at the same time. An improvement of the selectivity by increasing the temperature is, in principle, admittedly possible but this has a negative effect on the loading of the carbon dioxide with cholesterol and cholesterol esters and on the quality of the product obtained.